Push-to-talk (PTT) communication is half duplex communication over a network configured to support communication between members of a group of users of the network in which each of the group can acquire exclusive status as a “sender” and transmit information in a multicast mode to all the others in the group. For convenience of presentation, a period of time during which the PTT communication takes place is referred to as a PTT session. A communication network or portion thereof configured to support a PTT session and participants of the session, are referred to as a PTT network and comprises at least two participants and generally more than two participants.
When a given participant of a PTT session has active status as a sender, the other participants of the PTT session are referred to as “listeners”. Status as a sender during the session may generally be acquired by any of the PTT session participants at any time when no participant in the session is a sender by appropriately signaling the network. Once acquired, sender status is maintained until relinquished. Signaling to acquire sender status is obtained and maintained by appropriately operating a communication device configured to support PTT communication over the network. Usually, the communication device comprises a button, hereinafter a “PTT button”, which a participant of the PTT session depresses to signal desire to acquire sender status, and maintains depressed to maintain sender status.
PTT communications using cellular mobile phones, conventionally known as Push-to-talk over cellular (PoC), is half duplex communication during a PTT session over a cellular phone network between participants, equipped with cellular phones, hereinafter “PoC phones”, that are configured to provide, in addition to regular cellular phone communication, PTT communication over the cellular network. A cellular phone network or portion thereof configured to support a PTT session and participants of the session, are referred to as a PoC network and comprises at least two participants and generally more than two participants. The acronyms PoC and PTT may be used interchangeably hereinafter.
Typical of PoC communication, a participant becomes a sender, by merely pressing a PTT button on his or her PoC phone and acquires exclusive ability to transmit information, generally a voice message encoded in a suitable format for transmission, in a multicast mode to all the other participants of the PoC network. While a sender is transmitting, i.e. as long as the sender maintains his or her PTT button depressed, all the other PoC participants have status as listeners and cannot interrupt or transmit information to the sender or any of the other participants. A given sender relinquishes exclusive status as a sender when the sender releases his or her PTT button, thereby ending the given sender's transmission. After the given sender's transmission is ended, a first participant to press the PTT button on his or her mobile PoC phone acquires status as a sender with exclusive ability to transmit to all the other participants of the PTT session. This form of one-way half-duplex communication, contrasts with full-duplex communication, typical of cellular mobile communication and most forms of telephone communication, in which both the sender and the listener are able to transmit information to one another, or a third party, simultaneously.
In a typical PoC environment, all the participants in a PTT session use PoC phones equipped with a same type of CODEC (encoder/decoder) adapted to operate using a same voice encoding/decoding format. When a participant is a sender, the CODEC in the sender's PoC phone converts the sender's voice into signals, hereinafter “PTT signals”, having a format, hereinafter a “PTT format”, suitable for transmission over the PoC network. The CODEC in a listener's PoC phone that receives the senders PTT signals translates the PTT format back into voice.
Nevertheless, there may be PoC situations in which a sender and a listener are equipped with PoC phones comprising different types of CODECs, i.e. CODECs configured to use different types of coding/decoding PTT formats, so that the listener's PoC phone, also referred to as a receiver, does not “understand” the PTT format transmitted by the sender's PoC phone. As a result, the receiver is unable to translate the received PTT format into voice. Such situations can arise for example, when participants subscribing to different PoC network operators attempt to communicate in a PTT mode with each other.
To deal with such situations, some PoC networks have a network infrastructure comprising transcoders. The transcoders generally comprise relatively large Digital Signal Processing (DSP) equipment located at network gateways (communication exchange terminals), and are adapted to convert a PTT format used by a first CODEC into a different type of PTT format used by a second CODEC. A drawback to this approach is cost associated with using DSPs, which can be substantial for PoC networks involving large numbers of participants. Another approach is to fit a plurality of CODECs into participants' PoC phones, each CODEC capable of encoding/decoding a PTT format used by a different PoC network operator. Here again, the cost of fitting multiple CODECs in PoC phones for a large number of participants can be substantial.
Another approach to providing PTT communication between PoC phones equipped with different CODECs involves configuring the PoC phones with multiple decoders compatible with the different voice encoding formats of the different CODECs. Each such PoC phone comprises a single encoder and multiple decoders. Although it is generally less expensive to implement multiple decoders in the handsets rather than a plurality of “complete” CODECs, such a solution can also be expensive.
US Patent Publication 2006/0034260 A1, “Interoperability for Wireless User Devices with Different Speech Processing Formats,” the disclosure of which is incorporated herein by reference, describes providing interoperability between wireless user devices using different CODECs. Interoperability is achieved by equipping communication devices with a plurality of decoders, each capable of decoding a different speech encoding format.
US Patent Publication 2006/0120350 A1, “Method and Apparatus Voice Transcoding in a VoIP Environment,” the disclosure of which is incorporated herein by reference, describes a method for voice transcoding in a voice-over-internet-protocol (VoIP) environment comprising: receiving packets that include vocoder data frames in which source voice samples have been encoded according to a first vocoding format; decoding, by a decoder, the vocoder data frames to produce a sequence of linear speech samples; obtaining, by an encoder via a non-circuit switched communication path, linear speech samples from the sequence of linear speech samples produced by the decoder; and encoding, by the encoder, groups of speech samples from the sequence of linear speech samples to produce vocoder data frames according to a second vocoding format.